[Foundational agents] Enabling individual agents - UI to update settings on top-namespace and instance level

Update groups/{namespace}/-/settings/gitlab_duo and gitlab duo settings to include the ability to turn on or off individual agents:

• Latest design: https://www.figma.com/board/hOiNqnzdqAOiBhn7oYPM64/%F0%9F%9A%A7--19119-Permissions---Governance?node-id=366-1349&t=s8bYogATOtih7vF1-0#1513719550

• The list of foundational agents can be fetched with FoundationalChatAgents.all